The present invention relates to radiofrequency identification (RFID) markers for detection of surgical implements and, more particularly, to an RFID marker embedded in or otherwise securely attached to a surgical implement such as a laparotomy pad or sponge, metallic surgical instrument or other implement and which is specifically adapted for preventing the inadvertent retention of such implement(s) during a surgical procedure.
Included in the prior art are many patents that disclose systems and methods for detection of surgical implements following surgery prior to wound closure. Such detection methods incorporate x-ray opaque markers within surgical implements and effect detection using postoperative x-ray of the patient or of discarded sponges. Also disclosed for detection of surgical implements are methods involving use of resonant tags made from magnetomechanical elements, capacitors, LRC oscillatory circuits and smart markers.
U.S. Pat. Nos. 4,114,601 and 4,193,405 to Abels disclose a medical and surgical implement detection system. Surgical implements such as metallic instruments, sponges, implantable devices and indwelling therapeutic devices and materials are detected within the human body or other area of interest by incorporating or adding a radiofrequency transponder. A microwave system mixes two fundamental microwaves having 4.5-5 GHZ frequencies and relies on a non-linear transponder to produce higher order product frequencies. The transponder may be a thin film of a ferrite material exhibiting gyro-magnetic resonance at selected frequencies or a solid-state device containing diodes and field effect transistors. A non-linear transponder signal is received by a receiving antenna and filtered to remove all fundamental microwave frequencies. Unfortunately, substantially all of the higher order microwave frequencies generated by the transponder are readily absorbed by the human body. Consequently, most of the higher order microwave frequency signals are lost before any non-linear transponder can be detected. In addition, the gyro-magnetic effect produces a relatively weak signal.
U.S. Pat. No. 4,658,818 to Miller, Jr., et al. discloses an apparatus for tagging and detecting surgical implements. A miniature battery-powered oscillator is attached to each surgical implement and activated prior to its initial use. The output of each oscillator has the form of a low powered pulse of 1-10 MHZ frequency, and is coupled to the body's fluids and tissue. Following surgery but prior to suturing, a detection system senses for any pulses generated by the oscillator within the body. The surgical implement detection system disclosed by the '818 patent is not passive. It requires a miniature battery, which is turned on at the beginning of the operation. When the operation is complete, the battery may have already discharged, in which event the surgical implement will not be detected by the apparatus.
U.S. Pat. No. 5,057,095 to Fabian discloses a surgical implement detector utilizing a resonant marker for use in human or animal tissue. The marker is triggered into resonance by the interrogating field. A resonance frequency signal emitted by the marker is detected by a separate detection circuit adjacent to the interrogating circuit. The marker resonates due to magnetostriction properties of an amorphous metal ribbon, a piezoelectric device or a tuned LRC circuit. The response from the marker constitutes a simple sine wave having a particular frequency, which is less than one gigahertz. A detector is responsive within an interrogation zone encompassing a surgical wound. The marker is adapted to undergo resonance solely at a pre-selected frequency below 1 GHz, causing a substantial change in its effective impedance. An electromagnetic dipole field is thereby generated, which produces an identifying signal identity. The interrogation means is also provided with a means for varying phase and/or direction of the interrogating field. A receiving means placed within the interrogation zone detects the “ring-down”, phase-shift, impedance or other identifying characteristic of the element in resonance.
U.S. Pat. No. 5,188,126 to Fabian, et al. discloses a surgical implement detection system utilizing capacitive coupling for use in human or animal tissue. The system comprises a battery-powdered marker, which is secured to the surgical implement and positioned within a surgical wound. A detection means has an antenna disposed in close proximity of the tissue. Means are provided for capacitance coupling of the marker with the antenna and activation of the battery-powered marker. A field generating means associated with the detection system generates an electromagnetic field having a predetermined frequency band ranging from about 10 MHz to 1 GHz. The electromagnetic field causes the marker to produce a signal in the form of a sinusoidal wave having unique signal identity. A battery powers the capacitive marker, which will not function when the battery is discharged. Inasmuch as there is no means to verify the status of the battery, this method for detection of surgical implements is vulnerable to battery failure.
U.S. Pat. No. 5,190,059 to Fabian, et al. discloses a surgical implement detector utilizing a powered marker for use in human or animal tissue. A battery-powered marker is secured to a surgical implement positioned within the wound. An electromagnetic field generating structure in the battery-powered marker is provided for generating within the transmitting zone an electromagnetic field having a predetermined frequency band, providing the marker with signal identity. The response from the battery-powered marker is a simple sine wave having a particular frequency. Such a response does not comprise a digital code as it lacks the capacity for identifying a surgical implement. Battery power is required such that detection is not effected when the battery is discharged.
U.S. Pat. No. 5,541,604 to Meier discloses transponders, interrogators, systems and methods for elimination of interrogator synchronization requirement. A Radiofrequency Identification (RFID) system has an interrogator and a transponder, the interrogator having a first tuned circuit of a powering frequency for sending a powering burst to a transponder, a filter/demodulator for receiving a wireless, modulated RF response from a transponder. The interrogator additionally has a second tuned circuit in electrical communication with a modulator. The second tuned circuit has a selected bandwidth about a communication frequency. The selected bandwidth does not substantially overlap the powering frequency and encompasses the bandwidth of the modulated carrier of the RF response. The carrier is modulated using pulse width modulation (PWM), pulse position modulation (PPM), frequency-shift keying modulation (FSK), or another type of modulation methods. The interrogator also has a controller in electrical communication with the filter/demodulator and the tuned circuits. It enables the first tuned circuit to send the powering burst during a first time period and enables the modulator in electrical communication with the second tuned circuit to receive the RF response during a second time period. The transponder has a tuned circuit. A tuning circuit in electrical communication with the tuned circuit modifies the frequency characteristics of the tuned circuit. The circuit is thereby tuned during the powering burst to the powering frequency. It is also tuned during the RF response to the communication frequency. The transponder also includes a demodulator in electrical communication with the tuned circuit for receiving the RF interrogation therefrom and for demodulating data from the RF interrogation. This current generation RFID device sends a preset code to the interrogator. It is powered entirely by the power burst signal provided in the first time period and is capable of transmitting the code at a high rate to the interrogator.
U.S. Pat. No. 5,664,582 to Szymaitis discloses a method for detecting, distinguishing and counting objects. A marker made from a nonmagnetostrictive strip of amorphous or crystalline material produces higher harmonic excitations when energized by an alternating magnetic field. The higher harmonics are detected by the exciting antenna. This passive, non battery-powered device receives a fixed second harmonic frequency sinusoidal signal based on the size, shape and material of the marker. Information is not digitally encoded and therefore the marker has no means for identifying individual counting objects.
U.S. Pat. No. 5,931,824 to Stewart, et al. discloses an identification and accountability system for surgical sponges and includes machine-readable information located on a plurality of surgical sponges used in the surgical procedure. At the end of an operation the surgical implements are machine read to determine whether any of the sponges are missing. The system also includes an x-ray detector for the detection of missing sponges. Detection of sponges placed within a surgical wound is not effected unless the absence of a sponge is detected during the sponge count procedure following surgery. Actual location of a missing sponge requires x-ray examination.
U.S. Pat. No. 6,026,818 to Blair, et al. discloses a tag and detection device. An inexpensive tag has the form of a ferrite bead with a coil and a capacitor, or a tag of flexible thread composed of a single loop wire and capacitor element. The detection device locates the tag by pulsed emission of a wide band transmission signal. The tag resonates with a radiated signal, in response to the wide band transmission. Resonation occurs at the tag's own single, non-predetermined frequency, within the wide band range. The pulsing action of the wide band transmission builds the non-predetermined, radiated signal intensity over the ambient noise levels. This radiated signal is a sinusoidal wave of non-predetermined frequency and does not have digital information that identifies a particular sponge or surgical pad.
U.S. Pat. No. 6,076,007 to England, et al. discloses surgical devices and their location. A surgical device, such as a catheter or a prosthesis, carries, at a predetermined location, a tag composed of a high permeability, low coercivity magnetic material having a magnetized bias element. The tag is interrogated with a rotating magnetic field. Interaction between the tag and the rotating magnetic field is detected by a flying null system to determine the location of the tag within the human or animal body. Typically, the marker will be in the form of a thin film, a wire or a strip. The response signal from the tag is a sinusoidal wave with no digital information. The detection system is based on flying null technology. The tag is used for locating a catheter tip, not a sponge or surgical pad within a surgical wound.
U.S. Pat. No. 6,424,262 and U.S. patent application No. 20040201479 to Garber, et al. disclose applications for radiofrequency identification systems. An RFID target is used, together with magnetic security element and a bar code reader, to check out and manage library materials such as reference books, periodicals, and magnetic and optical media. This disclosure has nothing to do with detecting sponges or surgical pads in a surgical wound.
U.S. Pat. No. 6,838,990 to Dimmer discloses a system for an excitation leadless miniature marker. An excitation field excites a leadless marker assembly. The system comprises a source generator assembly having a power supply, an energy storage device, a switching network and an untuned source coil interconnected and configured to deliver a selected magnetic excitation signal waveform, such as continuous bipolar or unipolar waveform, or a pulsed magnetic excitation signal waveform. The power supply is configured to deliver power to energize the energy storage device. The switching network is configured to: direct electrical current through the source coil. It alternately switches between a first on position and a second on position. Stored energy is alternately transferred from the energy storage device to the source coil and from the source coil back to the energy storage device. The source coil is coupled to the switching network to generate an excitation signal. Untuned excitation is used by the source coil to look for resonance from a set of markers embedded in human tissue. Information is processed using an array sensor to three-dimensionally locate a given marker. This system does not locate sponges or surgical pads misplaced in a surgical cavity. The frequency response of a target is sinusoidal and has no digital capability.
U.S. patent application No. 2002/0143320 to Levin discloses tracking medical products with integrated circuits. Radiofrequency identification devices comprising a microprocessor, memory, analog front end and antenna are used to communicate with a remote unit. The remote unit has a processor memory and transreceiver that receives digital data from radiofrequency identification devices attached to medical products, such as a pharmaceutical product, a blood product or a tissue product. The radiofrequency identification device is first scanned and then rescanned at the end of the surgical procedure. There is no indication that the radiofrequency identification devices are encapsulated. Neither is there any indication that the RFID devices are incorporated in a sponge, surgical pad or surgical implement. Further, there is no indication in the Levin application that the RFID devices are scanned during surgery to establish the location of the sponge or surgical pad. There is also no indication in Levin application that the RFID devices are scanned at the end of an operating procedure to establish that no sponges or surgical pads are left behind in a surgical cavity.
U.S. patent application No. 2003/0006878 to Chung discloses a smart tag data encoding method. Information is stored in a smart tag having a memory. The smart tag has two memory portions. One of the partitions is permanent and cannot be erased. A second memory portion stores application specific data. The second memory portion also stores a relational check number, which validates the integrity of the data stored in the second memory, thereby detecting memory alteration or corruption. This smart tag data encoding method has nothing to do with detecting a sponge or surgical pad left behind in a surgical wound.
U.S. patent application No. 2003/0057279 to Uozumi et al. discloses an identifying system for an overlapped tag. An RFID and one or more resonance capacitors connected through on-off switches may be turned on or off by a remote control circuit. The overlapping tags may be interrogated using an RFID system, or one more resonance capacitors. The Uozumi et al. system does not detect sponges and surgical pads in a surgical wound, since they are not expected to overlap. Signals from the resonant capacitors of Uozumi et al. form a sine wave comprising electromagnetic radiation and do not carry a digital code
U.S. patent application No. 20030066537 to Fabian, et al. discloses a surgical implement detection system. Surgical implements used during an operating procedure are detected in human tissue. Markers attached to the surgical implements change their impedance at a preselected frequency in the presence of an electromagnetic field. The system uses a magnetomechanical element which vibrates at a preselected frequency when excited. This preselected frequency, when detected, indicates the presence of a surgical implement to which the magnetomechanical marker element is attached. The marker resonates only at a fixed frequency and provides no digital information suited for identifying a sponge or a surgical pad.
U.S. patent application No. 20030105394 to Fabian, et al. discloses a portable surgical implement detector. Surgical implements used during an operating procedure are detected in human or animal tissue. Markers attached to the surgical implements change their impedance at a preselected frequency in the presence of an electromagnetic field. Each of the markers is thereby provided with signal-identifying characteristics. The portable detector sweeps the surgical cavity with a range of frequencies which excites and vibrates markers attached to surgical implements at preselected frequencies, causing their detection. The markers resonate at preselected frequencies in the form of sinusoidal waves, but do not provide digital data suited for identifying a sponge or surgical pad.
U.S. patent application No. 20030192722 to Ballard discloses a system and method of tracking surgical sponges. The sponges have a radiopaque object embedded therein which is visible when the sponges are x-rayed. All sponges removed from the surgical wound are placed into a sponge container which is provided with an internal device to x-ray and identify the sponges after use. However, because the sponges are not x-rayed when first put into use and because it is not possible to x-ray the sponges when they are in the patient wound, the Ballard system is incapable of determining whether all sponges have been removed from the patient wound or whether any sponges have been left behind in the patient wound.
U.S. patent application No. 20040129279 to Fabian, et al. discloses a miniature magnetomechanical tag for detecting surgical sponges and implements. This tag is a magnetomechanical device and is excited by the interrogating magnetic field. The interrogating field is switched off, and the ring down characteristic of the resonant target is detected. The system does not provide digital means for identifying a sponge or surgical pad.
U.S. patent application No. 20040250819 to Blair, et al discloses an apparatus and method for detecting objects using tags and a wideband detection device. An apparatus and method for the detection of objects in the work area, such as surgical sites, including a detection tag affixed to objects used during surgery, is disclosed. The apparatus and method feature interrogates with a transmitter emitting a pulsed wideband signal, prompting the tag element to provide a return signal, which is received and analyzed. The device features an antenna portion containing a single or a plural ring-shaped antenna. Also, the pulsed wideband interrogation signal may be pulsed-width modulated or voltage-modulated. The pulsed signals trigger a continuing response signal from the tag in its response frequency range, which increases in intensity to the point where it becomes differentiable from background noise and is detected within the wideband range by the signal detector as an indication of the presence of the tag. The tag is excited by a wide band pulsed interrogation signal, which builds up the output of the tag and can be detected over ambient electronic noise. The tag signal has a predetermined frequency in the form of a sinusoidal wave, and does not carry digital information suitable for identifying laparotomy pads or sponges retained within the wound cavity.
U.S. patent application No. 2005/0003757 to Anderson discloses an electromagnetic tracking system and method having a single-coil transmitter. The system includes a single coil transmitter emitting a signal, a receiver receiving a signal from the single coil transmitter, and electronics for processing the signal received by the receiver. The electronics determine a position of the single coil transmitter. The transmitter may be a wireless or wired transmitter. The receiver may be a printed circuit board. The electronics determine position, orientation, and/or gain of the transmitter. The single coil transmitter is a powered device and may be wired or wireless. It is not a passive device that can be incorporated in a sponge or surgical pad due to the requirement for a reliable power source.
PCT patent application No. WO 98/30166 to Fabian et al. discloses a surgical implement detector utilizing a smart marker. The surgical implement is appointed for disposition within human or animal tissue and is made to be electronically identifiable by affixing thereto a smart marker, which is an unpowered integrated circuit with EEPROM memory carrying a code. When the smart marker is sufficiently close to the reader antenna, a voltage is generated within the marker antenna that charges the capacitor and powers the integrated circuit. A switch is opened and closed to transmit the stored code in the EEPROM memory, providing identification and recognition of a smart target attached to a surgical sponge. The marker antenna operates at a frequency of near 125 KHz. The frequency of information transfer to the reader is very slow, due to the switching on and off action.
Despite the above noted deficiencies associated with RFID devices, certain industries have successfully implemented such technology for various purposes. For example, RFID technology has been successfully used to track cattle by the placement of RFID tags on cattle ears. The RFID tags may be read automatically or manually by a hand-held scanner in order to identify individual cattle. The cattle's identity may be linked to a computer database allowing access to a large amount of detailed information regarding the animal's origin, breeding, age and weight. Furthermore, such RFID tags may be utilized to identify the proximity of certain cattle to a feeding trough. Such RFID tags can be active, passive, or semi-active. Unfortunately, RFID systems such as those used in cattle tracking suffer from several critical deficiencies that detract from their overall utility. For example, RFID systems designed for cattle identification are understood to be limited to a range of just a few inches. Unfortunately, in surgical applications, a greater range is required. More specifically, in surgical applications, a range of at least 8 inches or more is required in order to adequately scan a patient's wound from above and reliably detect the presence of an RFID tag to which a surgical device may be attached.
Another deficiency of prior art RFID systems is that they are optimized to identify one or more RFID tags which are harmless to the environment being interrogated such as in a cattle yard, on a warehouse pallet, or in toll booth lane. In this regard, the primary goal of most RFID systems of the prior art is to successfully collect an identification message from the RFID tag. Detecting the mere presence of an RFID tag is typically of secondary importance.
However, in the surgical environment, these priorities are reversed. More specifically, in a surgical environment, it is of primary importance to detect the presence of all RFID tags such that the items to which they are attached may be removed from the patient wound. It is of secondary importance to identify the RFID tag. As such, the unique priorities of surgery means that the application of RFID detection systems for the surgical environment may involve non-obvious methodologies and system configurations.
Although at higher frequencies, (typically 13.56 MHz, 850 to 950 MHz, or 2.45 GHz), the added bandwidth permits the processing of multiple RFID tags at one time, RFID systems that operate in the low frequency ranges such as at 125 kHz typically allow for the stimulation of only one nearby RFID tag at a time. Once the RFID tag is stimulated, a signal reader may then retrieve a digital ID code impressed upon the signal. Unfortunately, the presence of two or more RFID tags within range of the detector generally results in a failure to acquire identification codes from any of the RFID tags due to “data collision” between the RFID tags. In this regard, current RFID readers are generally incapable of determining the presence of multiple RFID tags within a scanned area or of determining the identification code of any one of the RFID tags in an area containing multiple RFID tags.
The above-mentioned deficiencies of current RFID readers could unfortunately mean that either two or more RFID tags are present in the area, or, that there are no RFID tags present in the area being scanned. As such, there is currently no reliable method using conventional RFID tagging technology to verify whether or not surgical items are present after the end of an operation (i.e., prior to wound close) absent the incorporation of more expensive collision-control RFID tag technology. The failure to adequately identify and remove such items prior to wound closure is fairly widespread and well-documented in medical literature. Unfortunately, inadvertent retention of surgical items in the patient can result in serious complications for the patient and even death.
Another deficiency of prior art RFID systems is that the range of RFID tag detection is dependent upon the degree to which the RFID reader and the RFID tag are aligned with one another. When the antenna coils of the RFID tag and the RFID reader are aligned for best energy coupling, detection range is as much as 50-100% greater than when the antenna coils are oriented at 90° relative to one another. Unfortunately, there is no way to determine the orientation of the RFID tag which may be hidden from view in the patient wound. Therefore, detecting a tagged surgical item may be unsuccessful if the RFID reader antenna is not optimally-oriented with respect to the unseen RFID tag.
As so noted, the ability to detect an RFID tag may be compromised due to misalignment between the RFID tag antenna and the remote detector unit antenna. The occurrence of this event has been very low (less than 5 percent) and does not occur when individual readings are obtained. Nonetheless, to counteract the possibility of misalignment, the installation of two or more RFID tags on the same surgical implement may eliminate this event. Unfortunately, the installation of multiple RFID tags on the same surgical implement will result in data collision between the RFID tags and therefore requires that anti-collision measures be taken.
One solution to the above-mentioned problem is the incorporation of anti-collision technology. More specifically, with anti-collision technology, an identification code may be retrieved from two or more RFID tags in a scanned area during simultaneous interrogation of multiple RFID tags. Such anti-collision technology operates by delaying the response of each RFID tag by an appropriate amount of time in order to avoid simultaneous responses at the signal reader which, in turn, avoids corruption of signal data from the RFID tags. Unfortunately, this delay in RFID tag response increases the power requirements for each RFID tag. In a passive system, a limited amount of power is typically collected from the signal transmitted by the RFID reader (i.e., interrogator) such that a battery may be additionally required to provide power for the extended duration due to signal delay.
In addition to the added power requirements, a further deficiency associated with anti-collision technology is that such systems are typically more costly than RFID tag systems that operate on a one-at-a-time basis because they require the tags to have read/write capability. The increased cost of anti-collision technology in the RFID detection system may be prohibitive when the instrument or implement to which an RFID tag is attached is less expensive than the RFID tag itself.
As can be seen, there remains a need in the art for a highly reliable, surgical implement detection system wherein RFID tags may be attached to laparotomy pads or sponges and other non-metallic items as well as metallic instruments or implements for detection thereof. Preferaby the surgical implement detection RFID tag is passively powered (i.e., non-battery powered). Also needed is a marker of the type described above which can withstand cleaning and sterilization procedures commonly employed, and resists exposure to body fluids such as blood or saline solutions. Additionally, a surgical implement marker and corresponding detection device, is needed to provide a reliable indication of the location of foreign objects within a surgical wound during and at the completion of a surgical procedure prior to wound closure.
Furthermore, there exists a need in the art for a reliable detector system that utilizes RFID technology and which is specifically configured to provide an indication about the presence of multiple RFID tags in a specific area such as within a surgery wound. More specifically, there exists a need in the art for an RFID detector system that is capable of indicating whether one or more RFID tags are present within a given range or, alternatively, whether no RFID tags are present within the range. Even more specifically, there exists a need in the art for an RFID detector system that accurately and reliably detects the mere presence of one or more RFID tags within a surgical wound and preferably at a range of at least 8 inches with at least a 95 percent probability of an accurate determination of presence or non-presence.
Also, there exists a need in the art for an RFID detector system that allows for an indication of the surgical implement or instrument (i.e., via the identification code of the RFID tag) once located such that the surgical item can be inventoried. Additionally, there exists a need in the art for an RFID detector system that preferably operates at a relatively low frequency such as at 125-134 kHz in order to minimize the detrimental effects encountered in the upper frequencies, including increased signal attenuation by body tissue and nearby metallic objects. In addition to these disadvantages encountered in the upper frequency range, further drawbacks are encountered as the Gigahertz range is approached. As is well known in the art, microwave ovens typically operate at this frequency to heat watery foods and can therefore potentially cause unwanted localized heating (i.e., cooking) of body tissue by inducing rapid vibration of water molecules contained therewithin. The low frequency range, on the other hand, is not only less affected by intervening tissue and metal, but has the added benefit of avoiding issue heating. Lastly, there exists a need in the art for an RFID detector system that is of low cost such that the detector system is feasible for implementation in hospitals having large quantities of surgical items and implements.